Sinclair ZX80

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Sinclair ZX80
Image:ZX80.jpg
Type	Home computer
Released	1980
Discontinued	1981
Processor	Z80 @ 3.25 MHz (most machines used the NEC μPD780C-1 equivalent)
Memory	1 kB (16 kB max.)
OS	Sinclair BASIC

The Sinclair ZX80 was a home computer brought to market in 1980 by Sinclair Research of Cambridge, England. It was notable for being the first computer available in the United Kingdom for under a hundred pounds (a pricetag of £99.95, to be exact). It was available in kit form, where purchasers had to assemble and solder it together, and as a ready-built version at a slightly higher cost for those without the skill or inclination to build their own unit. The ZX80 was very popular straight away, and there was for some time a waiting list of several months for either version of the machine.

The machine was designed by Jim Westwood around a Z80 @ 3.25 MHz<ref>This frequency was critical, as the TV picture generation depended on it (see ZX81).</ref>, and was equipped with 1 KB of static RAM and 4 KB ROM containing the Sinclair BASIC programming language, editor, and "OS". BASIC commands were not entered by spelling them out; instead, the commands were selected rather like they would be on a scientific calculator — each "key" had several different functions activated by use of several modifier (shift) keys.

Display was over a RF connection to a household television, and simple offline program storage was possible using a cassette recorder. The video display generator of the ZX80 used very minimalist hardware plus a combination of software to generate a video signal. As a result of this approach the ZX80 could only generate a picture when it was idle, i.e. waiting for a key to be pressed. When running a BASIC program, or even when pressing as key for any input, the display would, therefore, black out momentarily to support the function. This made moving graphics difficult since the program had to introduce a pause for input to display the next change in graphical output. The later ZX81 improved on this somewhat because it could run in a 'slow' mode while creating a video signal, or in a 'fast' mode without generating a video signal (typically used for lengthy calculations).

A ZX81 8 kB ROM was available to upgrade the ZX80 and cost around 20% of a full blown ZX81. It came with a thin overlay keyboard and ZX81 manual. Simply taking off the top cover of the ZX80 and prising the old ROM from its socket and carefully inserting the new ROM and adding the keyboard overlay, the ZX80 (now ZX81) would now function almost identically to the proper ZX81 except for SLOW mode, and this was purely down to hardware differences. The process was easily reversed to get the ZX80 back to its old self.

Sinclair also produced RAM expansion packs for the ZX80; the original ZX80 RAM Pack held either 1, 2 or 3 kB, a later model held 16 kB, both were built around dynamic RAM chips (DRAM). There was no upgrade for the monochrome display however.

The machine was mounted in a tiny white plastic case, with a one-piece blue membrane keyboard on the front; it owed its distinctive appearance to industrial designer Rick Dickinson. There were problems with durability, reliability and over-heating. The entire system was about the size of two paperback books placed beside each other. Crude it might have been, but the ZX80 was a true innovator and it kick-started the 1980s home computer craze in the UK and New Zealand. It was superseded by a number of other Sinclair machines, notably the Sinclair ZX81 and the very successful ZX Spectrum.

Sales of the ZX80 reached about 50,000 — an unheard of number for the day which contributed significantly to the UK leading the world in home computer ownership through the 1980s. Owing to the unsophisticated design and the tendency for the units to overheat, surviving machines in good condition are quite uncommon and can fetch high prices by collectors.

[edit] Internal workings

The ZX80 was designed around TTL chips while the successor ZX81 used a semi-custom chip (an ULA or Uncomitted Logic Array), but these were superficial differences — the hardware and system programs (except the BASIC versions) were very similar, with the only significant difference being the NMI-generator necessary for slow mode in ZX81. See ZX81 for technical details.